1. Field of the Invention
The present invention generally relates to sub-irrigation systems and, more particularly, to a new capillary carpet irrigation system and the method of manufacturing thereof.
2. Description of the Prior Art
Sub-irrigation systems where plants in pots are placed upon capillary mats which provide water through capillary action into the bottom of a permeable pot are well known in the art.
A significant advantage of the sub-irrigation system is that no further equipment is required other than that already at the disposal of producers who generally use overhead sprinkler irrigation systems.
The sprinklers are used to water the plants and any water falling between pots is captured by the capillary mat. The water saturated capillary mat thereafter, provides water on demand through capillary action from the roots and permeable base of the pot resting on the capillary mat. Sub-irrigation allows water to be provided according to the needs of each plant on demand since water is drawn up under capillary action by the roots and permeable pot base resting on the saturated capillary mat.
Therefore, sub-irrigation on capillary mats is a viable alternative that meets the objectives of a closed system namely, elimination of runoff water and environmental risks associated and efficient use of water and fertilizers over conventional systems. Sub-irrigation on capillary mats generally involves maintaining the capillary mats at or near saturation point in order to provide the plants with a constant supply of water. Water moves from the saturated mat to the pots, soil substrate and roots by capillary ascent.
However, due to several disadvantages, the use of capillary mats has traditionally been restricted to greenhouse applications. For example, the water held by the mat often evaporates from the surface and constitutes a net loss in addition to contributing to salts accumulation, nutrients, etc. on the mat surface itself. In humid greenhouses however, where there is a high relative humidity and absence of air movement, evaporation is not a major problem in contrast to field conditions. In an open field, algae and weeds will rapidly grow in the exposed surface of the capillary mat. As well, in an open field the low relative humidity of the air, solar heat radiation and high air movements will result in high evaporative losses. As result therefore, these drawbacks have limited the interest in sub-irrigation practices for outdoor use in nurseries. Although sub-irrigation can eliminate runoff in the environment, the net result is a decrease in water use efficiency due to high evaporative losses.
To address the problem of surface evaporation and accompanying salt accumulation on the capillary mat, and to limit algae growth and weed growth in the capillary mats, prior art systems have included a porous perforated plastic sheet on the top surface of the capillary mat. The perforated sheet allows rain water and irrigation sprinkler water to flow through the perforations into the capillary mat. The perforated sheet also allows water to flow out of the capillary mat into the bottom of permeable pots resting on the mat. While dark colored perforated plastic sheets have been very efficient in preventing algae growth in the capillary mat, they still allow significant evaporation from the surface to the extent that evaporated losses exceed losses experienced through recycling or standard irrigation with no recycling. The stored water surface is directly under the top perforated sheet in such prior art carpets, and evaporative loss through the perforated sheet is prohibitively high.
This problem has been addressed in U.S. Pat. No. 6,178,691 issued on Jan. 30, 2001 to Caron et al., the content of which is herein incorporated by reference. U.S. Pat. No. 6,178,691 discloses a four layer irrigation carpet, including an impervious base membrane, and a permeable top membrane enveloping a water bearing rigid porous mat and an overlying resilient compressible coarse porous mat. The compressible mat is resiliently compressible under each pot and where compressed, it defines a plurality of localized capillary action conduits between the water bearing rigid mat and each water permeable pot through the permeable top membrane. The resilient compressible mat when decompressed has a negligible capillary rise and serves to inhibit evaporative water loss from the underlying rigid mat. The pores of the compressible mat impede air circulation immediately above the upper surface of water held in the water bearing rigid mat, The air within the compressible mat pores immediately above the rigid mat therefore have a high humidity and water vaporisation at the surface is therefore inhibited by the high vapour concentration of air in the compressible pores. Air circulation within the compressible mat is impeded by the inherent resistance of the porous structure. Thus, water vapor escape from the water surface in the rigid mat through the perforations of the top membrane is impeded reducing evaporative water loss, even when used in outdoor applications.
While the capillary carpet disclosed in the above-mentioned patent constitutes a major improvement over conventional capillary carpets, it has been found that when installed on greenhouse surfaces or directly on the soil in a field, drainage and, thus, loss of stored water occurs, resulting in a loss of efficiency of the carpet. Poor capillary contact may also exist with some very coarse growing media if free water (water with no tension) is not present at the mat surface in an early stage of capillary rise. As soon as a little slope exists though, drainage conditions are created and watering the mat results in location having water under tension at all times. The lowest point in the field will determined the tension. This tension prevents good capillary rise with coarse media and may induce stresses to the plant, generally resulting in yield losses to the grower. The water contained in the mat will flow by gravity from the highest point to the lowest point in the field, thereby withdrawing water from the sections of the mat which are located on the highest point. This will also cause water contained in the pots located on these highest sections of the mat to be submitted to a suction force, resulting in a portion of the water in the pots to be drained off.
There is thus a need to find a way of avoiding important water tension to be created even though the carpet is laid down on a sloped supporting surface. There is also a need to improve capillary rise in coarse growing media.